A comparison between high- and low-energy ion mixing at different temperatures

High-energy ion mixing occurs when an ion beam of a few hundred keV bombards an interface under the surface. Low-energy ion mixing arises when an ion beam of a few keV bombards an interface near the surface during, e.g., sputter depth profiling and low-energy ion-assisted deposition. At low temperatures, the rate of both high- and low-energy ion mixing can be influenced by thermodynamic parameters, such as the heat of mixing and the cohesive energy of solids. These effects are demonstrated by ion mixing experiments using metallic bilayers consisting of high-atomic-number elements. A model of diffusion in thermal spikes is used to explain this similarity. Low-energy ion mixing can also be strongly affected by surface diffusion and the morphological stability of thin films. These effects are illustrated using results obtained from sputter depth profiling of Ag/Ni, Ag/Fe, and Ag/Ti bilayers at elevated temperatures. High-energy ion mixing at low temperatures can be influenced by the anisotropic momentum distribution in a collision cascade as seen from a set of marker experiments to determine the dominant moving species in high-energy ion mixing. An understanding of these similarities and differences between high- and low-energy ion mixing at different temperatures will provide useful guidelines for applications of ion mixing.